The squiggly lines are caused by leafminers. The larvae from some flies, moths or beetles feed between the upper and lower leaf surfaces. They make the squiggly lines while tunneling through. Citrus leafminers are a potentially serious pest. The "mines," those squiggly lines, can result in leaf curling.
You can prune off and destroy the branches that are damaged, but don't place these cuttings in your regular yard waste recycling. Put the infested branches in your regular household garbage. This way the infected branches will not become mulch at a yard waste processing facility.
After pruning, water and fertilize the plant so it can outgrow the damage. It's tough to manage leafminers with chemical control, because they are protected inside the leaf. At the first signs of leafminer feeding, take chemical action. There can be several generations that overlap in the course of a year because a generation can be completed in three weeks.